vhost-scsi: Take configfs group dependency during VHOST_SCSI_SET_ENDPOINT

This patch addresses a bug where individual vhost-scsi configfs endpoint
groups can be removed from below while active exports to QEMU userspace
still exist, resulting in an OOPs.

It adds a configfs_depend_item() in vhost_scsi_set_endpoint() to obtain
an explicit dependency on se_tpg->tpg_group in order to prevent individual
vhost-scsi WWPN endpoints from being released via normal configfs methods
while an QEMU ioctl reference still exists.

Also, add matching configfs_undepend_item() in vhost_scsi_clear_endpoint()
to release the dependency, once QEMU's reference to the individual group
at /sys/kernel/config/target/vhost/$WWPN/$TPGT is released.

(Fix up vhost_scsi_clear_endpoint() error path - DanC)

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: <stable@vger.kernel.org> # 3.6+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 69906ca..a17f118 100644 (file)
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -1312,6 +1312,7 @@ static int
 vhost_scsi_set_endpoint(struct vhost_scsi *vs,
                        struct vhost_scsi_target *t)
 {
+       struct se_portal_group *se_tpg;
        struct tcm_vhost_tport *tv_tport;
        struct tcm_vhost_tpg *tpg;
        struct tcm_vhost_tpg **vs_tpg;
@@ -1359,6 +1360,21 @@ vhost_scsi_set_endpoint(struct vhost_scsi *vs,
                                ret = -EEXIST;
                                goto out;
                        }
+                       /*
+                        * In order to ensure individual vhost-scsi configfs
+                        * groups cannot be removed while in use by vhost ioctl,
+                        * go ahead and take an explicit se_tpg->tpg_group.cg_item
+                        * dependency now.
+                        */
+                       se_tpg = &tpg->se_tpg;
+                       ret = configfs_depend_item(se_tpg->se_tpg_tfo->tf_subsys,
+                                                  &se_tpg->tpg_group.cg_item);
+                       if (ret) {
+                               pr_warn("configfs_depend_item() failed: %d\n", ret);
+                               kfree(vs_tpg);
+                               mutex_unlock(&tpg->tv_tpg_mutex);
+                               goto out;
+                       }
                        tpg->tv_tpg_vhost_count++;
                        tpg->vhost_scsi = vs;
                        vs_tpg[tpg->tport_tpgt] = tpg;
@@ -1401,6 +1417,7 @@ static int
 vhost_scsi_clear_endpoint(struct vhost_scsi *vs,
                          struct vhost_scsi_target *t)
 {
+       struct se_portal_group *se_tpg;
        struct tcm_vhost_tport *tv_tport;
        struct tcm_vhost_tpg *tpg;
        struct vhost_virtqueue *vq;
@@ -1449,6 +1466,13 @@ vhost_scsi_clear_endpoint(struct vhost_scsi *vs,
                vs->vs_tpg[target] = NULL;
                match = true;
                mutex_unlock(&tpg->tv_tpg_mutex);
+               /*
+                * Release se_tpg->tpg_group.cg_item configfs dependency now
+                * to allow vhost-scsi WWPN se_tpg->tpg_group shutdown to occur.
+                */
+               se_tpg = &tpg->se_tpg;
+               configfs_undepend_item(se_tpg->se_tpg_tfo->tf_subsys,
+                                      &se_tpg->tpg_group.cg_item);
        }
        if (match) {
                for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) {